Loud speaker



May 2 HOPKINS LOUD SPEAKER 2 Sheets-Sheet 1 Filed June 11. 1925 1 INVE OR 774F605 C/70P/r/A 5 BY mm; BM; mm M V ATTW May 24,1927. 1,630,011

. M. C. HOPKINS LOUD SPEAKER Filed June 11, 1925 2 Sheets-Sheet 2 INVENTOR #471606 C floP/fims BY $QA LAMW 1/ MW F M A TTORNEY6 Patent ed May 24, 1927..

UNITED STATES PATENT OFFICE.

MARCUS G. HOPKINS, F BROOKLYN NEW YORK, ASSIGNOR, BY DIRECT AN'D MESNE ASSIGNMENTS, TO HOPKINS GORIPORATION, A CORPORATION OF DELAWARE.

' LOUID SPEAKER.

Application filed. .Tune 11, 1925. Serial No. 36,563.

This invention relates to electrical reproducing instruments, and more especially to loud speakers of the conical diaphragm type. A device embodying theinvention can be used advantageously with radio receiving sets, and also is suited to line wire reception, and to various other uses as will be understood by those skilled in the art.

I have discovered that fibrous diaphragms of the conical type can be markedly improved in clarity of tone by placing the diaphragm under radial tension. The loud speaker described in detail in the accompanying specification explains one way in which that discovery can be used to advantage. I

It is an object of the present invention to provide a fibrous diaphragm of the conical type. which while stiff and resistant to distortion is nevertheless so supported that it can move bodily under the action of an elec trieal translating movement having a short stroke. ly making the cone of the right kind of fibrous material, and tensioning that material as hereinafter described, and supporting the cone in such a way as to give it freedom of bodily movement, and by corre lating, with such a cone so supported an electrical movement havinga powerful but short stroke, I am able to produce results which in my opinion are far superior to those obtainable from loud speakers of the i conical diaphragm type now regularly on the market.

It is a further object of the Present invention to so mount the cone and its actuating movement that the loud speaker as a whole can be readily mounted in a box or cabinet, such, for instance, as the cabinet of a phonograph, or the like.

, Other objects and advantages will become clcarfrom the following detailed descriptionivhich is to be taken in conjunctionvwith the accompanying drawings wherein I Fig. 1 is a rear elevational View of a loud speaking instrument in accordance withthis invention, y p

Fig. 2 1s a cross+sect1onalview taken approximately along the vertical center line of Fig. 3 is a fragmentary elevational view, partlyin cross-section, showing details of construction of the electromagnetic actuat- "-ing mechanism,i 1

which the electromagnetic actuating mecha- Fig. 4 is a cross-sectional view taken along the line 44 of Fig. 3,

Fig. 5 is a fragmentary elevational View of the peripheral portion of a conical diaphragm, illustrating one way in which the periphery of the diaphragm is slitted and partly cut away so as to form a considerable number of relatively small sectors which may be easily bentinto the desired plane,

Fig. 6 is a cross-sectional view of the peilapheral portion of the diaphragm shown in Figs. 7 and 8 are elevational and crosssectional views respectively showing the peripheral portion of the diaphragm illustrated in Figs. 5 and 6, but bent into a plane which is normal to the axis of the diaphragm,

Figs. 9 and 10 are elevational and crosssectional views of the peripheral portion of the diaphragm slitted radially but in which 70 the sectors thereby formed have not been cut away as in the case of the diaphragm of Figs. 5 to 8, inclusive, and

Figs. 11 and 12 are elevational and crosssectional views similar to Figs. 9 and 10, but showing the sectors bent into a plane normal to the axis of the diaphragm.

Inasmuch as the loud speaker of the present invention is especially suited for incorporation in the structure of an ornamental 8o cabinet, I have here shown it equipped with a cabinet of portable character. It will be clear that a much larger and more elaborate cabinet could be provided, as, for instance, when the loud speaker is built in as a permanent adjunct to an elaborate radio receiving set.

In Figs. 1 and 2, the rectangular wooden framework 1. together with the covers 2 and 8 form a casing structure for the loud speaking instrument which comprises a conical diaphragm {1, anelectromagnetic actuating mechanism 5. and a cast metal spider 6, to which the diaphragm 4 is attached and on nism 5 .is'mounted". The conical diaphragm 4 is preferably of large diameter-generally more than nine inches-fand is preferably made of very light, but,rigid,.pap.er so that itmaybe caused tovi'brate bodily with litthe or-no, distortion. .Inorder that'the diaphragm may not be restrained against vibratory movement anymore than is necessary, the peripheral portion is slitted radially as illustrated in Figs. 9, 10, 11 and 12 wherein the radial slits arerepresented by reference numeral 4. In Fig. 9 the slits 4" are shown closed as a result of the fact that the sectors formed by these slits are lying in the plane of the cone as indicated by Fig. 10.

In Fig. 11 the slits 4* are shown open.- the openings being the result of the sectors being bent into a plane normal to the axis of the cone as indicated by Fig. 12. The edges of the peripheral sectors are secured to the peripheral rim of spider 6. This may be accomplished by cementing As indicated at 4 in Figs. 1 and 2 there is a considerable margin betweenthe inner edge of the spider rim to which the cone is attached and the inner radius of the peripheral sectors. The marginal portion 4 bends quite readily thereby permitting free bodily vibratory movement of the cone. In order to further weaken the resistance to vibration, the pe ripheral'sectors of the diaphragm may be cut away -as indicated at 4* in Figs. 5 and 7. The triangular openings formed by cutting away the sectors may be as large as desired providing sufficient material is left to properly support. the diaphragm.

Not all grades of paper are suited for use as a diaphragm material. The paper should be stifl. It should be porous and light in weight. A long fibered paper of porous structure and free from loading will serve well, and any sizing should be of the fibers before felting and not of the sheet after it has been formed up; A layer of varnish or other like material applied to a finished cone is likely to impair greatly its sound producing qualities. Brittleness in the cone is a desirable characteristic, provided the paper has at thesame time sufficient toughness to withstand commercial transportation and ordinary handling during use.

It has beenmy'experience that paper several years old is better than new stock, presumably because of an increased stiffening of the fibers due to aging. In any event the paper, or other fibrous material, used for the cone"must be capable of being bent without breaking in order that there may be formed in it the peripheral rim by which it is attached to the spider, and in order that it may have the requisite flexibility at the base of the cone to permit of relatively free bodily movement desired by me.

In making the diaphragm illustrated a fiat sheet of paper is first cut or punched to form a sector ofithe required radius and angle. Its periphery may be slotted and notched at the same time. The flat sector is then rolled up into a cone either by hand or through the aid of suitable mechanical devices, and is then glued along its radial joint. The peripheral tongues tire then bent as indicated by Figs. 8 and 12 so that they will all lie in substantially the same plane and form a flat rim for the cone.

The next operation consists in gluing this rim to the flat. face of the spider. I prefer to wet the spider with glue or cement and set the cone down on it, and then after the adhesive has commenced to set I grip the edge of the spider between my thumb and forefinger and press dpwnwardly and outwardly on each paper tongueto slide it outward far enough to place a very sensible ra dial tension on the cone. All of the tongues are thus slipped outward over the half set adhesive. Mechanical devices may be used for effecting this radial 'tensioning of the cone if desired. a

In addition to this radial tensioning the cone is tensioned on all circles concentric with its axis by the mere act of rolling the paper into a cone preparatory to gluing its radial joints. Consequently, after the tongues have been pulled outward, and the glue has set, the cone will be under tension both radially and circumferentially. This I have found greatly improves its tone producing qualities. Radial tensioning of the cone gives a slight inward bend to each radius of the cone, and though this is not enough to be readily detected by the eye, it can easily bedetected by the ear of a user.

As an alternative procedure for putting the cone under radial tension, it is possible to dampen the cone before gluing it to the spider, and then let it shrink as its moisture content comes down to normal. Such an operation, however, must be carefully conducted for otherwlse the cone will buckle and will be stressed in an irregular and troublesome manner,'sometimes even to the extent of bulges or depressions in the surface. time for moistening and drying will help.

Also I have successfully tensioned cones by wetting the formed and glued cone with a formaldehyde solution, or an astringent, to shrink the paper somewhat. By virtue of the inherent. lightness and stiffness of the paper and its circumferential and radial tensioning andlthe flexibility of the bend at which the cone is joined to the tabs constituting the rim, the diaphragm is able to vibrate substantially as a whole and with little or no bending or distortion of the cone proper. The stiffness ofthe cone permits the use of an electrical movement having a short stroke, and the freedom from restraint makes the cone so sensitive that the expenditure of but a small amount ofpower is neededto give satisfactory audibility.

The spider 6 is secured at its mm bymeans of four wood screws 7 to a wooden partition 8, which is secured to the inside of frame 1. The spider G-isformed with an open rectangular center portion to which The use of a humidor and plenty of the electro magnetic actuatingmechanism is attached. By reason of the skeletonized formation of the spider the actuating mechanism is readily accessible.

The electrical movement disclosed herein cooperates well with a cone so constructed and mounted, for when its armature or reed is connected to the apex of the cone through a rigid ba-r attached to the armature near itsiniddle, there is delivered to the cone an impulse of short range and considerable power, and it is to such impulses that a tensioned and freelysupported cone most readily responds. Novel features of the electrical movement are claimed in my copending applications'Serial No. 35,425 filed June 6, 1925 and Serial No. 36,562, filed June 11'. 1925.

The electrical movements or electro magnetic actuating mechanism comprises a U- shaped permanent magnet 9, to each extremity of which is secured an angle iron 10, 11. To the angle iron 10 is attached a bifurcated soft iron pole shoe 12, between the arms of which is inserted a specially formed member 13 of molded insulating material'such as hard rubber or bakelite. The member 13 is provided with openings into each of which is inserted an electromagnet coil 14, 15. In the arms of the soft iron shoe 12 there are secured threaded studs 16, 17 which function as adjustable polepieces. The unthreaded portions of these studs extend through the centers of the coils 14, 15, respectively, and are slotted to reduce eddy currents. A rigid soft iron or steel armature 18 is rigidly attached at one end to the angle iron 11being preferably riveted thereto as shown-and its free end portion is disposed substantially midway betweenthe opposing ends of the pole pieces 16,17. At a point along the midway portiono'f armature 18 there is secured a rod or connecting link 19, one end of which is attached to the cone 4. The connection between the link 19 and cone 4 is made through'the medium of a hollow bolt 20, through which the link' 19 passes and in which the link may be secured by a transverse set screw. In order to prevent damage to the' paper cone, its central portion is secured between two metal conical washers 21,22 which are clamped together by means ofthe' bolt 20 andfnu t 23.

. The actuating mechanismi'forms a, self by'means of machine screws 25. a

Normally, that is to say, when no current is "flowing in coils 14,; 15, both adjustable pole pieces 16, 17 are: of the same magnetic polarity and of equal strength. The arma tui'e '18 being "disposed 7 mid-way between contained unit and is attached to the spider these pol'efpiecesit attracted by both .of

themfle'qually The gaps between pole pieces 16, 17 and the armature 18 are adjustable and may readily be so adjusted that the best results are obtained under any predetermined conditions. The best results should be obtained when the normal magnetic attraction between one pole piece and the armature is equal and opposite to the magnetic attraction bet-ween the other pole piece and the armature.

If the instrument is operated through'a transformer and has no normal direct current flowing through its coils it will generally be found that the two air gaps may be equal or substantially so. But if there is a normal direct current flowing through its coils, as is the case when it is connected directly in the output circuit of a vacuum tube amplifier, it may be found necessary to adjust one or both of the air gaps so that they are not equal when no current flows.

When the current flowing through coils 14, 15 fluctuates, the equilibrium of magnetic forces acting on the armature becomes upset and the armature is accordingly attracted toward one or the other pole pieces, depending upon the character of the current fluctuation. The amplitude of movement of the armature is proportion to the amplitude of the current fluctuation. Accordingly, if the current fluctuations correspondm with sound waves, the armature will vibrate with the same frequency and with an amplitude proportionate to the amplitude of the sound waves which caused the current fluctuations. The vibrations of the armature are short and powerful. The armature being of steel and relatively stiff and thick has a natural period above audibility. The natural elasticity of armature 18 is sufficient to permit the flexing of it, but the armature is so stiff and so supported at one end that it cannot strike the adjustable pole toward which it moves. The exact point at which rod 19 can best be attached to armature 18 lies about midway of the length of the armat-ure and depends somewhat on the thickness and stiifn'ess of the armature, and on the weight and other characteristics of the diaphragm to which rod 19 is rigidly attached. The exact point can best be found by trial.

Whatever kind of cone is used with the electrical movement here disclosed, best results, according to my experience, can be had by'giving tothe cone as a whole a freedom of bodily movement and a freedom from local bending and distortion' Radial tensioning will help. By thus co-ordinatingthe diaphragm to the electrical movement a highly satisfactory-loud speaker can be obtained.

Its tonal characteristics can be varied somewhat by changing the weight or stifiness of the vibratory armaturefor reed, or by changing the weight, size or thickness of the fibrous cone.

In the drawings, the covers eacheonsist of a narrow frame to which is attached what may be conveniently termed an open work grill 31, consisting of woven cane. Any sort of perforated cover may be utilized, but the woven cane presents an attractive appearance, is durable, and adds but little to the weight of the instrument;

.Electrical connections are made to the instrument through the medium of a conductor cord 26, terminal block 27, conductors 28,

29 and a pair of binding posts 30, which may 1 venient means for lifting and carryin be secured to the members 13. p

' A hinged liftingring 32 provides aconthe instrument and when not in use is practically out of sight.

parts all of which may be easily manufactured and quickly assembled without the need for any unusual skill.

The instrument is designed with a view to its being used as shown or, alternatively,

built into a cabinet such, for example, as a talking machine cabinet. Its form lends itself particularly Well for the latter purpose.

I claim.

1. In a translating device,'a conical fibrous 35 sound producing diaphragm tensioned radially, and a support, said diaphragm having a rim secured to said support for a part only of its width and flexibly connecting the diaphra m to the support to give the cone relative Ereedom for axial movement.

2. In a translating device, a conical fibrousl sound producing diaphragm tensioned radially, and a support, said diaphragm having a flat rim secured to said support for a. part only of its width and flexibly connecting the diaphragm to the support to give the cone relative freedom for axial movement.

3. In a translating device, a conical fibrous sound producing diaphragm tensioned radially, and having ,a fiat supporting rim consisting of a plurality of tabs integral with the cone. v

4:. In a translating device a conical fibrous sound producing diaphragm tensioned radially and having a flat supporting rim consisting of a plurality of under-cut tabs, substantially as described.

5. In a translating devicefthe combination of a conical sound producing diaphragm tensioned radially and having a flat supporting rimaconsistin of a plurality of tabs, and a support for sai diaphragm contacting with a part only of each tab.

6. In a translating device, the combination of-a conical fibrous sound producing diaphragm having a slotted'rim, the portions of the rim between the slots bein bent at an angle with respect to the wal s of the cone, and a support for said diaphragm contacting with a part only of said rim.

7. In a translating device, the combination of a conical diaphragm having a plurality of integral under-cut tabs, bent at an angle with respect to the walls of the cone, and a support for said diaphragm contacting with a part only of each tab.

8. In a translating device, the combination of a diaphragm tensioned radially and having a plurality of integral tabs each of which is under-cut at its base to give the cone greater freedom of axial movement, and a support for said diaphragm contacting with a part only-of each tab.

9. In a translatin device, the combination of a fibrous sound producing diaphragm having aslotted rim, a support for said diaphragm contacting with a part only of said rim to give the cone relative freedom for axial movement, and an actuating device 0peratively connected with the apex of the cone to act thereon with a short and relatively powerful stroke, substantially as described.

10. In a translating device, the combination of a conical fibrous sound producing diaphragm tensioned radially and havin a flat support-ing rim consisting of a plurafity of tabs integral with the cone, a support for said diaphragm contacting with a part only of said rim and allowing relative freedom of axial movement to said cone, and an actuating device operatively connected to the apex of said cone and operable thereon with a short and relatively powerful stroke, substantially as described.

11. In a loud speaker, a large conical diaphragm made of light weight stifi' paper, the peripheral portion of said diaphragm being divided by radial slits to form a considerable number of peripheral sectors, said sec tors being bent into a plane substantially normal to the axis of said diaphragm, a supporting member for said diaphragm, sald sectors being secured to said member, said diaphragm being rendered substantially free to vibrate bodily by reason of the division of its peripheral portion, and actuating mechanism for said diaphragm.

12. In a loud speaker, a large conical diaphragm, a supporting member comprising a circular rim, the peripheral portion of said diaphragm being radially slitted to form a lurality of perlpheral sectors, said sectors ing bent into a plane substantially normal to the axis of said diaphragm, said sectors being attached at their outer edge portions to said rim, certain of said sectors being reduced in cross sectional area between the points at which'they join the main body of said diaphragm and the points of attachment- -Inn ' sectional area of said sectors,

' center portion,

, mounted on said to said rim the resistancqto bodily vibration of said diaphragm being reduced by'reason of the reduction of cross and actuating mechanism for said diaphragm.

13. In combination, a rectangular casing having two perforated sides, and a lou speaker mounted within said casing, said instrument comprising a large conical iaphragm made of light means for resiliently supporting said phragms by its periphery so that stantially free to vibrate bodily, said supporting means inc ding a spider havin a substantially circular rim and a rectangu ar an actuating mechanism rectangular center portion, and a connecting link between said actuating mechanism and said diaphragm.

substantially weight stiff paper,

it is sub- 14. In a loud speaker, a receptacle comprising a frame, said frame being provided with a partition havin a circular opening, a spider mounted in sai frame and supported by said partition, a said spider, actuating means mounted on said spider and connected to said diaphragm, an open-work cover side of said frame.

15. In a translating device, the combination of a conical brous diaphragm, a support, and actuating means operatively connected with the apex of the conical diaphragm, said diaphragm being tensioned radially independent of said actuating means and being held in its state of tension by said support. I

In testimony whereof I aflix my signature MARCUS C. HOPKINS.

and secured to at leastone diaphragm carried by 

